The present invention relates to a stored-program control computer and more particularly to such a computer that includes program transfer control instructions in a noncontrol program area of memory.
Control devices have been developed which use a stored-program microcomputer to control various devices such as power plant, i.e., internal combustion engine or the like, in an automotive vehicle. Such a computer uses a memory in which a control program is previously written. This program has been read, instruction by instruction, by a central processor unit (CPU) to provide control of the controlled device. The CPU has a program counter having a count that sequentially increases to sequentially change an address to be referenced in the memory; the address value is altered for jump instructions, subroutines, etc.. If such a computer is used under conditions where external disturbances, such as electrical noise from the ignition system in an automotive vehicle, occur, various registers or counters in the CPU are often disturbed, leading to malfunction of the computer. The program contains instructions written in the memory, each of which instructions includes several steps, the number of which varies according to the instruction. The external disturbances are likely to affect the program instructions causing the CPU to read an incorrect instruction. For example, disturbing the value in a program counter may cause addresses used for accessing instructions or numerical data to be read as numerical value or instruction addresses, respectively. As a result the program control of the program goes wrong and may cause the computer to run wild beyond control.